In this study, we analyzed the effects of regional hydrologic variability during warm season (June-September) in South Korea due to ENSO (El -Southern Oscillation) pattern changes over the Tropical Pacific Ocean (TPO). We performed composite analysis (CA) and statistical significance test by Student`s t-test using observed hydrologic data (such as, precipitation and streamflow) in the 113 sub-watershed areas over the 5-Major River basin, in South Korea. As a result of this study, during the warm-pool (WP) El year shows a significant increasing tendency than normal years. Particularly, during the cold-tongue (CT) El decaying years clearly decreasing tendency compared to the normal years was appeared. In addition, the La years tended to show a slightly increasing tendency and maintain the average year state. In addition, from the result of scatter plot of the percentage anomaly of hydrologic variables during warm season, it is possible to identify the linear increasing tendency. Also the center of the scatter plot shows during the WP El year (+17.93%, +26.99%), the CT El year (-8.20%, -15.73%), and the La year (+8.89%, +15.85%), respectively. This result shows a methodology of the tele-connection based long-range water resources prediction for reducing climate forecasting uncertainty, when occurs the abnormal SSTA (such as, El and La ) phenomenon in the TPO region. Furthermore, it can be a useful data for water managers and end-users to support long-range water-related policy making.